Currently, the United States has 4,565 military personnel in Iraq who are training, advising and assisting Iraq's military in the fight against ISIS, with a current authorized troop ceiling of 4,647. With the increase, the authorized number of troop for Iraq rises to 5,262.
Carter made the announcement to reporters while traveling in Albuquerque, New Mexico. "In anticipation of the Mosul fight, the United States and the government of Iraq have agreed that additional U.S. and coalition capabilities could help accelerate the campaign at this critical phase," he said in a statement. "At the request of myself and Chairman [Joseph] Dunford and with the support and approval of [Iraqi] Prime Minister [Haider al-]Abadi, President Obama has authorized approximately 600 additional U.S. troops to further enable Iraqi forces."
According to Carter, the additional troops "will provide specific capabilities, including logistics and maintenance support; train, advise and assist teams for Iraqi security forces and Kurdish peshmerga for the upcoming Mosul operation; and expanded intelligence resources to help disrupt [ISIS'] terrorist network in Iraq and beyond."
In a statement posted on his official website, Abadi said the additional troops would "provide support for security forces and the Iraqi heroes in the fight looming in the liberation of Mosul." He emphasized that the American troops would continue to serve as advisers and that the combat mission to liberate Mosul would be conducted by Iraqi troops.
According to Pentagon spokesman Capt. Jeff Davis, the additional American troops will arrive in Iraq in a matter of weeks. Most will be maintenance and logistics personnel.
He said the majority of the new troops will be going to Al Asad Air Base in western Anbar province, which is lacking in infrastructure for growing operations in that province as the Mosul operation gets underway.
They will work to improve the airfield at Al Asad to enable night operations and instrument landings for the Iraqi and coalition aircraft operating from the base.
Additional logistics personnel will head to Qayarrah West, an air base in northern Iraq, where several hundred U.S. troops are already helping to prepare a major logistics hub for a Mosul offensive.
Davis said some personnel will go to other locations in Iraq that he declined to identify. He described the latest troop increase as "long anticipated and long planned. We've known that there would be a final additive number of capabilities prior to the final push."
Senior U.S. military officials have said in recent weeks that training has been completed for the eight to 12 Iraqi and Kurdish peshmerga brigades that will be used in the offensive to retake Mosul.
They have said that the Iraqi government is prepared to launch an operation in October to press toward Mosul, if the Iraqi government decides to move forward with that plan.
An estimated 3,000 to 4,500 ISIS fighters remain in Mosul, where they have been building up defenses in preparation for an Iraqi military offensive.
The vast majority of American troops in Iraq, about 3,765 of them, are in support roles for the Iraqi military. The number of U.S. military advisers in Iraq is about 100 personnel, plus 450 serving as military trainers. An additional 800 protect American personnel and facilities.
Wednesday's rise will be the 10th increase in the number of American troops since 275 U.S. service members were deployed to Baghdad in June 2014 as ISIS approached the city.
The Associated Press contributed to this story.